MOLECULAR ENGINEERING OF TRIGONAL OCTUPOLAR … · 1 MOLECULAR ENGINEERING OF TRIGONAL OCTUPOLAR...

1

MOLECULAR ENGINEERING OF TRIGONAL OCTUPOLAR MATERIALS

BASED ON 2,4,6-TRIS-DIARYLAMINO-1,3,5-TRIAZINES

By

Taner Gokcen

A Thesis Submitted to the Faculty of

Department of Chemistry and Biochemistry

Worcester Polytechnic Institute

Worcester, MA 01609-2280, USA

In partial fulfillment of the requirements for the

Degree of Master in Science

In Chemistry

By

August 24, 2005

Approved:

Dr. Venkat R. Thalladi, Advisor

Approved:

Dr. James W. Pavlik, Department Head

2

Abstract: Molecular engineering of some 2,4,6-(substituted biarylamino)-1,3,5-triazines

and crystal data belonging to the products 2,4,6-(m,m’-ditolylamino)-1,3,5-triazine, 2,4,6-

(p,p’-ditolylamino)-1,3,5-triazine and 2,4,6-(phenyl-p-tolylamino)-1,3,5-triazine were

reported. Retrosynthetic analysis of trigonal octupolar networks led to the identification

of tris-substituted diarylamino-triazines as molecular analogs of Piedfort units formed by

cofacial dimers of 2,4,6-triaryloxy-1,3,5-triazine molecules. Synthesis of mono and

diarylamiono triazines is achieved by coupling of the corresponding anilines with

cyanuric chloride. Synthesis of diarylamines exhibiting different functional groups on

two phenyl rings is attempted; the successful attempt in the case of phenyl-p-tolylamine

is described. All the crystals obtained so far belong to centrosymmetric space group

P21/c. Though none of the molecules retain trigonal symmetry in the crystal structures,

pseudo-trigonal assembly of molecules is identified in some cases. The assembly of

molecules within the crystals results in columnar structures formed by C-H..N and C-H..π

interactions.

3

Acknowledgements

I would like to sincerely thank my advisor Prof. Venkat R. Thalladi for his outstanding

support and patience during this research. I appreciated the opportunity to work with him.

The scientific fundamentals that I learned from him will build my future academic career

and my life.

I would like to thank to Prof. John C. MacDonald for his support and guidance. I also

would like to thank my friends and colleagues Veysel Yigit, Salimgerey Adilov, Marta

Dabros, Kasim Biyikli, Katarzyna Koscielska, Jason Cox, Nantanit Wanichacheva,

Hubert Nienaber, Somchoke Laohhasurayotin, and Chuchawin Changtong.

Finally I thank all chemistry and biochemistry faculty and graduate students for making

my stay at WPI an educational and enjoyable experience.

4

Table of Contents

Abstract 2

Acknowledgements 3

Table of Contents 4

List of Figures 5

List of Tables 8

Introduction 9

Results and Discussion 20

Experimental Section 55

Synthesis of diphenylamines 25

Synthesis of tris-phenylamino-triazines 27

Synthesis of tris-diarylamino-triazines 28

Crystallization 30

2,4-6-(m,m’-ditolylamino)-1,3,5-triazine 32

2,4-6-(p,p’-ditolylamino)-1,3,5-triazine 39

2,4-6-(p--ditolylamino)-1,3,5-triazine 47

Summary and Conclusion 58

References 74

5

LIST OF FIGURES Figure 1 Schematic representation of dipolar organic NLO materials 9

Figure 2 (a) Geometry of second-harmonic generation. (b) Energy-level diagram

describing second-harmonic generation 12

Figure 3 p-Nitroaniline (p-NA): prototype of a dipolar organic NLO molecule 12

Figure 4 3-Methyl-4-nitropyridine-1-oxide (POM) 13

Figure 5 Guanidinium route typeoctupolar molecule: crystal violet 14

Figure 6 TATB route type octupolar molecule:

1,3,5-triamino-2,4,6-trinitrobenzene 14

Figure 7 Schematic representation of idealized octupole 15

Figure 8 H-Bonding in the trigonal network of 1,3,5-tricyanobenzene 16

Figure 9 Figure 9. N,N,N-trimethylisocyanurate 17

Figure 10 Retrosynthetic analysis of trigonal octupolar network 18

Figure 11 List of triazines studied by Desiraju et al 19

Figure 12 Examples of trigonal octupolar materials 21

Figure 13 2,4,6-Triaryloxy-1,3,5-triazines 22

Figure 14 Retrosynthetic analysis for triaryloxy-triazines 23

Figure 15 Retrosynthetic analysis for tridiphenylamino-triazines 24

Figure 16 Schematic representation of synthesis of diphenylamines 25

6

Figure 17 List of diphenylamines used 26

Figure 18 Schematic representation of synthesis of tris-substituted-triazines 27

Figure 19 List of amines used 28

Figure 20 List of phenols used 28

Figure 21 Schematic representation of synthesis of tris-diphenylamino-triazines 29

Figure 22 List of tridiphenylamino-triazines obtained 29

Figure 23 Picture of MDMETZ molecule in crystal 32

Figure 24 Hexagonal structure formed by MDMETZ molecules 34

Figure 25 Picture of MDMETZ crystal view down [100] 35

Figure 26 Picture of MDMETZ crystal view down [010 36

Figure 27 Picture of MDMETZ crystal view down [001] 37

Figure 28 Picture of MDMETZ interactions view down [100] 38

Figure 29 Picture of MDMETZ view down [001] 39

Figure 30 Picture of PDMETZ molecule in crystal 41

Figure 31 Picture of PDMETZ crystal view down [100] 41



Figure 34 Picture of PDMETZ view down [001] 44

Figure 35 Picture of C-H..N bonding in PDMETZ crystal view down [100] 45

Figure 36 Picture of interactions in PDMETZ crystal view down [100] 46

Figure 37 Picture of PMETZ molecule in crystal 49

Figure 38 Picture of PMETZ crystal view down [100] 50


7


Figure 41 Picture of zig-zag shape formed by PMETZ view down [001] 53

Figure 42 Picture of interactions in PMETZ crystal 54

Figure 43 1H Spectrum of MDMETZ 59

Figure 44 13C Spectrum of MDMETZ 60

Figure 45 1H Spectrum of PDMETZ 61

Figure 46 13C Spectrum of PDMETZ 62

Figure 47 1H Spectrum of PMETZ 63

Figure 48 13C Spectrum of PMETZ 64

Figure 49 1H Spectrum of MMETZ 65

Figure 50 13C Spectrum of MMETZ 66

Figure 51 1H Spectrum of POHTZ 67

Figure 52 13C Spectrum of POHTZ 68

Figure 53 1H Spectrum of MMOTZ 69

Figure 54 13C Spectrum of MMOTZ 70

8

List of Tables Table 1.Geometrical parameters for C-H..π interactions found in the structures of

1-3 30

Table 2.Geometrical parameters for C-H..N interactions found in the structures of

1-3 31

Table 3.Crystallographic data for the structures of 1-3 31

Table 4.Dihedral angles between phenyl rings of MDMETZ molecule in crystal 33

Table 5.Dihedral angles between phenyl rings and central ring of MDMETZ

molecule in crystal 33

Table 6.Dihedral angles between phenyl rings PDMETZ molecule in crystal 40

Table 7.Dihedral angles between phenyl rings and central ring of PDMETZ

molecule in crystal 40

Table 8.Dihedral angles between phenyl rings of PMETZ molecule in crystal 47

Table 9.Dihedral angles between phenyl rings and central ring of PMETZ molecule in

crystal 47

9

Introduction Design and synthesis of organic materials exhibiting large second harmonic generation

(SHG) for the applications in the field of nonlinear optics (NLO) attracted intense interest

since Davydov and co-workers1 reported strong SHG from organic compounds having

electron donor and acceptor groups attached to a benzene ring in 1970. After screening a

wide variety of substituted benzenes for their SHG activity they came to the conclusion

that dipolar aromatic molecules possessing electron donor and electron acceptor groups

resulted in large SHG activity due to the intramolecular charge transfer between the two

groups with opposing electronic properties. It has become evident from this study that a

π-conjugated system possessing electron donor and acceptor groups will exhibit strong

SHG activity if it does not have an inversion center as represented in Figure 1. This

symmetry restriction is imposed upon even order NLO effects (such as SHG); materials

exhibiting odd order nonlinearities are not restricted by a center of symmetry.

Figure 1. Schematic representation of dipolar organic NLO materials.

It should be mentioned here that SHG activities of organic compounds were first reported

in 1964 by Rentzepis and Pao2 in 3,4-benzopyrene and Heilmer et al3. in hexamethylene-

tetraamine. Since then, the field of nonlinear optics has emerged as a major area of

research bringing together such faculties as physics, chemistry, and materials science

towards applications in photonics4-9 and optoelectronics.7,10,11

π-Conjugated System Acceptor Group Donor Group

10

Nonlinear optical effects arise when an intense electromagnetic field (in general laser

light) is illuminated on a material system. This intense radiation induces electrical

polarization within the material that results in new electromagnetic fields altered in

phase, frequency, or amplitude; that is, in optically nonlinear properties.

A relationship between the polarization (p) induced of a molecule and the applied electric

field E of incident electromagnetic wave at frequency ω can be written by:

p(ω)= α E1 + β E2+ γE3+ …

where p(ω) is the induced polarization in a microscopic medium (e.g., a molecule or ion)

at laser frequency ω; α is the linear polarizability; β is the first hyperpolarizability; γ is

the second hyperpolarizability; and E is the applied electric field component.

Analogously, the macroscopic polarization (P) induced in bulk media under intense

electromagnetic fields of a laser beam can be expressed in a power series as:

P(ω)= χ(1)E1 + χ(2 )E2 + χ(3) E3+ …

Here χ(1), χ(2), and χ(3) are the first-, second-, and third-order NLO susceptibilities,

respectively. The macroscopic second-order optical nonlinearities are related to their

corresponding microscopic terms β as follows:

χIJK(2) = N βijk ƒIƒ Jƒ K

where N is the molecular number density, ƒ is the local field factor due to intermolecular

interactions, and ijk and IJK represent directions along molecular and macroscopic axes.

11

First NLO phenomenon was reported by Franken et al.12 in a quartz crystal one year after

the first laser was developed by Maiman13 in 1960. In the beginning, most interest in

NLO materials was focused on inorganic materials;14-17 interest in organic materials

spurred after the work of Davydov et al.1 on dipolar aromatic compounds. The major

advantage of using organic materials for NLO applications lies in the inherent flexibility

in their synthesis; a large number of compounds possessing a range of geometries and

functional groups can be readily made using well-established synthetic chemistry. It

should be noted, however, that organic materials, in general, have limited thermal and

electrical stability.

This work describes materials that are designed to exhibit second-order NLO effects;

higher order effects are difficult to measure because higher order susceptibilities are

usually several orders of magnitude smaller than lower order ones. Much of current

interest in NLO materials is focused on the second- and third-order effects.

Figure 2 shows a prototypical second order NLO effect.18 When a noncentrosymmetric

material possessing second-order susceptibility (χ(2)) is illuminated with a laser light, the

output radiation contains waves of not just input frequency, but also doubled frequency.

This phenomenon is generally referred to as frequency doubling or SHG.

12

After the report of Davydov et al.1 most of the interest in organic NLO materials was on

p-nitroaniline-like19 (p-NA) (Figure 3) dipolar organic NLO molecules. Today p-NA is

accepted as the prototypical dipolar organic NLO material.

Even though dipolar organic NLO molecules exhibit large SHG activity, some problems

concerning NLO applications have been identified: (a) problems during crystallization of

long molecules; (b) problems in noncentrosymmetric self-assembly of molecules in

crystals due to favored anti-parallel stacking; (c) limited electrooptic configurations due

to high anisotropy in these molecules.

ω χ (2)

ω

2 ω

(a)

ω

ω

2 ω

(b)

NO2NH2

Figure 2. (a) Schematic representation and (b) energy-level diagram of SHG.

Figure 3. p-Nitroaniline (p-NA): prototype of a dipolar organic NLO molecule.

13

The second problem outlined above has been tackled in several ways such as introducing

directional hydrogen bonding interactions or chiral substituents. One eminent example

that uses a different strategy to generate acentric assembly includes POM (3-methyl-4-

nitropyridine-1-oxide)20 (Figure 4); in this molecule the nitroxide and nitro groups exhibit

similar push-pull characteristics but the molecule as a whole shows significant β values,

and the material shows large χ(2) values.

Despite the progress made in the dipolar NLO, the dipolar molecules are not best-suited

for NLO applications since their high anisotropy does not provide polarization

independence.21,22 Based on the experimental evidence23 as well as on general tensorial

and quantum-mechanical considerations,24 Zyss proposed that instead of dipolar

molecules more symmetrical molecules can self-assemble into more isotropic yet

noncentrosymmetric networks in two- and three-dimensions. He determined that these

molecules must have octupolar symmetry, and argued that these molecules can alleviate

the problems posed by dipolar molecules.25

N ONO2

H3C

Figure 4. 3-Methyl-4-nitropyridine-1-oxide (POM).

14

Zyss also proposed that octupolar materials can be prepared through three important

routes26-28: (a) Guanidinium Route (e.g. Crystal Violet, Figure 5); (b) σ-linkage (e.g. Si);

and (c) TATB route (e.g. 1,3,5-triamino-2,4,6-trinitrobenzene, TATB, Figure 6).

Since our interest is in “TATB route” type materials, it is represented schematically

(Figure 7). Molecular level octupoles are non-dipolar and non-centrosymmetric but one

has to ensure that noncentrosymmetric assembly is demonstrated in the crystal in other

words bulk noncentrosymmetry must be maintained. Octupoles show the polarization

independence and favor noncentrosymmetric assembly. Another advantage of octupoles

over dipolar molecules is that their β values increase as the extent of the charge transfer

increases, whereas in dipoles they increase to a maximum and then decrease as the bond-

length alternation increases.

Figure 6. TATB route type octupolar molecule

1,3,5-triamino-2,4,6-trinitrobenzene (TATB).

C

N(CH3)2

N(CH3)2

N(CH3)2

Figure 5. Guanidinium route type octupolar

molecule: crystal violet.

NO2

NH2

NO2

NH2

NO2

NH2

15

There are four factors affecting second-order optical nonlinearity:29 (a) conjugation

length; (b) strength of donor and acceptor groups; (c) nature of π-bonding sequence; (d)

substitution. Therefore main work in organic octupolar NLO materials is centered on

manipulating these four factors and further crystal engineering of such a molecule into a

noncentrosymmetric network. To design such acentric network one can identify

retrosynthetic routes as stated in the previous work reported by Thalladi et al.30 It must be

stated that following this trend is not trivial since majority of trigonal molecules routinely

adopt close-packed crystal structures of low symmetry, according to Kitaiigorodskii’s19

theory of close-packing. Also today, the importance of H-bonding in crystal engineering

is well known.20 Hydrogen bonds can enforce a preferred orientation better than charge-

charge or van der Waals interactions since they are moderately strong and directional.21

+q

-q

(a) (b)

Figure 7. (a) Schematic representation of (a) idealized octupole represented as a cube with eight point charges. (b) Projection of the cube along a body diagonal transforms it to a two-dimensional trigonal symmetric material (“TATB route”

octupole). The charges on the projected diagonal coincide and cancel out.

16

Etter has proposed the rules about the selectivity of different functional groups for

hydrogen bonding.22 Examples of hydrogen bonding making two-dimensional trigonal

symmetric networks are shown below (Figures 8 and 9).

H

C H

C

HC

N

N

N H

C H

C

HC

N

N

N

H

C H

C

HC

N

N

N H

C H

C

HC

N

N

N

Figure 8. 1,3,5-Tricyanobenzene.

17

Since three-dimensional structural control is difficult, we concentrated our interest in

two-dimensional noncentrosymmetric networks. A typical symmetry pattern is that of

trigonal molecules self-assembled into noncentrosymmetric structures as shown in

Figures 8 and 9. When Thalladi et al. used retrosynthetic analysis of a two-dimensional

noncentrosymmetric network A (Figure 10) to identify its structural units that are

assembled with intermolecular interactions, they discovered the desired microscopic

architecture B. They have identified crystalline triaryloxy substituted 1,3,5-triazines

forming stacked diads called Piedfort units, as their starting supramolecular synthons C.

N

N N

O

O

O

CC

C

H

H H

HH

H

H

H

H

N

N

N

O

O O

C

C

C

H

H

H

H

H H

H H

HN

N

N

O

O O

C

C

C

H

H

H

H

H H

H H

H

Figure 9. N,N,N-Trimethylisocyanurate.

18

On the basis of expected specific electrostatic interactions between phenyl rings, by

further retrosynthetic analysis they identified 2,4,6-triphenoxy-1,3,5-triazines D as

starting molecules for the generation of noncentrosymmetric trigonal octupolar networks.

In summary they reported crystal structures and NLO properties of molecules of a series

2,4,6-triaryloxy-1,3,5-triazines, 1-6 (Figure 11) that are stabilized by weak intermolecular

interactions such as C-H…O and C-H…N hydrogen bonding.

N

N

N

O

OO

N

N

N

O

O

O

R

R

R R

R

R

N

N

N

O

O

O

R R

R

A B

C D

Figure 10. Retrosynthetic Analysis of trigonal octupolar network (A) Trigonal network; (B) Recognition of trigonal species;

(C) Stacked molecular diads of triazines; (D) 2,4,6-triaryloxy-1,3,5-triazine.

19

In this work, based on the studies above, we proposed to create a molecular analog

(2,4,6-tris-(diphenylamino)-1,3,5-triazines) of the conceptual dimer formed from two

2,4,6-triphenylamino-1,3,5-triazines by stacking on each other.

N

N

N

O

OO

R1R3

R2

R1

R3R2

R1

R3R2

1 R1=R2=R3=H 2 R1=Cl R2=R3=H 3 R1=Br R2=R3=H 4 R1=CH3 R2=R3=H 5 R1=R2=Cl R3=H 6 R1=R2=CH3 R3=H 7 R1=R2=H R3=Cl 8 R1=R2=H R3=Br

Figure 11. List of triazines studied by Thalladi et al.

20

Results and Discussion

In the area of trigonal organic octupolar NLO materials, most of the studies focused on

the molecular level optimization, synthesis and characterization of the compounds. Both

by experimental results and also theoretical calculations it has been verified that

hyperpolarizability of an organic compound is related to several factors such as: 1)

conjugation; 2) length of π-conjugation; 3) strength of electron donor and acceptor

groups; and 4) substitution. Therefore, many researchers focused on the molecular level

chemistry of trigonal organic compounds in by manipulating these four factors.

Figure 12 (below) shows some examples that belong to the trigonal octupolar compounds

family. In molecular level they are all octupolar, noncentrosymmetric and show nonlinear

optical properties. One important issue is to carry over this molecular

noncentrosymmetry, to the bulk noncentrosymmetry, in other words to the

supramolecular level.

21

Figure 12. Examples of trigonal octupolar molecules.

OMe

OMeMeO

CN

CN

NC RR

RR

R

R

(a) (b)

Ru

NN

NN

N

N

NBu2

NBu2

NBu2

NBu2

Bu2N

Bu2N

N

OO

O

N NN

N

A

A

A

(c) (d)

R=4,4’-O(CH2)10-OC6H4C6H4CN

22

Being octupolar, these molecules have a zero ground-state dipole moment, so they are

predicted to favor the formation of noncentrosymmetric networks.

Thalladi et al. reported a series of 2,4,6-triphenoxy-1,3,5-triazines (Figure 13). These

molecules are very good examples of molecular level design by using crystal engineering

principles to obtain octupolar NLO materials. This study is also a good example of how

to carry over molecular noncentrosymmetry into two-dimensional bulk

noncentrosymmetry in crystal structure, where compound 1 (Figure 13) adopts a

noncentrosymmetric crystal structure with a measurable SHG powder signal.

Using retrosynthetic analysis they identified appropriate precursor trigonal molecules (D)

(Figure 14) based on the concept of the dimeric Piedfort unit (C) where two TAOT

molecule are stacked on each other.

N

N

N

O

OO

R1R3

R2

R1

R3R2

R1

R3R2

1 R1=R2=R3=H 2 R1=Cl R2=R3=H 3 R1=Br R2=R3=H 4 R1=CH3 R2=R3=H 5 R1=R2=Cl R3=H 6 R1=R2=CH3 R3=H 7 R1=R2=H R3=Cl 8 R1=R2=H R3=Br

Figure 13. 2,4,6-Triaryloxy-1,3,5-triazines.

23

In our work we intended to create molecular analogs of the conceptual dimer C that are

optimized both at molecular and supramolecular level. It has been reported by Thalladi et

al. that a typical symmetry pattern that leads to noncentrosymmetric two-dimensional

networks can be developed by using molecules having trigonal symmetry as templates.

We propose herein the retrosynthesis (Figure 15) of a two-dimensional network

generated by the conceptual dimer through herringbone interactions between aryl rings.

Further retrosynthesis let us identify tris-diarylamino-triazines as starting materials.

C D

N N

N O

O

O

R

R

R

Figure 14. Retrosynthetic analysis of 2,4,6-triaryloxy-1,3,5-triazines.

NN

NO

O

O

NN

NO

O

O

R R

R

R

R

R

24

A B

N N

N N

N

N

R R

R

RR

R

C

Figure 15. Retrosynthetic analysis for tris-diarylamino-triazines.

25

Our next goal was to synthesize this type of molecules and decide what type of R groups

to use. We aimed at polar, nonpolar, mono substituted, symmetrical disubstituted (both R

groups are same) and nonsymmetrically disubstituted (R1 and R2 are different) R groups

to get different varieties and also to observe the effects of substitution and the effects of

different R groups. Unfortunately, due to various constraints we were only able to

synthesize few of them.

Attempted Synthesis of Diphenylamines

The best way to obtain the desired triazines is to couple cyanuric chloride with

substituted diphenylamines. We began our work with an attempt to synthesize the desired

diarylamines by coupling of aryl halides with anilines (Figure 16). Figure 17 shows the

diarylamines we have been able to syntheisize; most of these were made only in small

quantities due to a range of synthetic and purification difficulties described below.

X

R1

NH2

R2

HN

R1R2

+

Figure 16. Schematic representation of synthesis of diphenylamines.

26

There are many papers in the literature reporting the synthesis of substituted diphenyl

amines; in general they follow the strategy (Figure 16) of using a mixture of catalyst,

base and solvent. We used mostly the copper based catalysts; others used palladium or

nickel with complex ligands and tedious reaction conditions. We attempted various

conditions with copper catalyst by using copper iodide, copper sulfate or copper bronze,

as well as changing base (K2CO3, KOt-Bu, KOH) and solvent. We also tried the

synthesis in pressure vessels without any catalyst in the presence of potassium t-butoxide.

It should be noted that for the mono-substituted diphenyl amines, there are two options:

desired functional group can be either on aryl halide or on aniline, in particular for the

synthesis of phenyl-p-tolylamine we tried the both ways. In addition, we attempted the

synthesis of p,p’-dihydroxydiphenyl amine from the acid catalyzed condensation of p-

aminophenol in the presence of benzenesulfonic acid. Unfortunately, most reactions

resulted in low yields and many byproducts, except in the case of the phenyl-p-

tolylamine.

1) phenyl-p-tolylamine 2) diphenylamine 3) N-phenylpyridin-4-amine 4) p-methoxydiphenylamine 5) p-chlorodiphenylamine 6) p,p’-dihydroxydiphenylamine

Figure 17. List of diphenylamines

27

Synthesis of Triarylamino-Triazines

Our aim was to synthesize tris-phenylamino-triazines and to use them as intermediates

for further synthesis of tri-substituted diarylamino-triazines, but we also considered the

opportunity to synthesize them as another family.

Synthesis of triarylaminotriazines can be achieved by coupling cyanuric chloride with

anilines (Figure 18). The anilines that were used are listed below (Figure 19), we also

tried some phenols (Figure 20) instead of anilines. In the case of 4-aminophenol and 3-

aminophenol, since they bear both amine and hydroxy functional groups, we found a way

in the literature to just react with amine group. We also tried to convert methoxy group of

the products 4-methoxyaniline and 4-methoxyphenol to hydroxy group using BBr3.

Figure 18. Schematic representation of synthesis of tris-substituted-triazines.

N

N

N

Cl

ClCl

NH2

R

N

N

N

N

NN

R

R

R

+

28

Synthesis of tris-Diarylamino-Triazines

Triazine family is well known in terms of synthesis. The reaction scheme (Figure 21) is

similar to triarylaminotriazines: coupling of substituted diarylamine with cyanuric

chloride at high temperatures (even though it is reported as first substitution occurs at 0

oC, second one at 25 oC and the third and last one at 67 oC, we got success over 200 oC)

results in the formation of the triazine product with vigorous formation of HCl as the

reaction progressed.

1) Aniline 2) p-toluidine 3) p-chloroaniline 4) p-bromoaniline 5) 4-aminopyridine 6) 2-amino-5-methyl-aniline7) p-amino-acetophenone 8) 3-chloro-4-methyl-aniline9) 4-methoxyaniline

1) 4-aminophenol 2) 3-aminophenol 3) methoxyphenol4) phenylphenol 5) p-cresol

Figure 19. List of anilines. Figure 20. List of phenols.

29

Since our aim was both to synthesize triazines and also analyze the effects of substitution

we decided to synthesize triazines with all kinds of functional groups, both symmetrical

(R1 and R2 are same) and unsymmetrical (R1 and R2 are different). But due to some

constraints we were only able to synthesize few of them, and they are listed below

(Figure 22). Products 1-6 have been purified, the remaining ones are still in process.

HN

R1 R2

N

N

N

Cl

Cl Cl

N

N

N

N

NN

R1

R1

R1 R2

R2

R2

+

Figure 21. Schematic representation of synthesis of tris-diphenylamino-triazines.

1) 2,4,6-(m,m’-ditolylamino)-1,3,5-triazine 2) 2,4,6-(p,p’-ditolylamino)-1,3,5-triazine 3) 2,4,6-(p-methyldiphenylamino)-1,3,5-triazine 4) 2,4,6-(m-methyldiphenylamino)-1,3,5-triazine 5) 2,4,6-(p-hydroxydiphenylamino)-1,3,5-triazine 6) 2,4,6-(m-methoxydiphenylamino)-1,3,5-triazine 7) 2,4,6-(N-phenyl-1-naphthylamino)-1,3,5-triazine 8) 2,4,6-(N-phenyl-2-naphthylamino)-1,3,5-triazine 9) 2,4,6-(p-nitrosodiphenylamino)-1,3,5-triazine 10) 2,4,6-(p-nitrodiphenylamino)-1,3,5-triazine 11) 2,4,6-(m-hydroxydiphenylamino)-1,3,5-triazine

Figure 22. List of tridiphenylamino-triazines obtained.

30

Crystallization

We tried to obtain crytals of the pure compounds by slow evaporation technique with

different solvents. All crystals we got belong to the monoclinic space group P21/c. Even

though they all belong to centrosymmetric space group, trigonal or pseudotrigonal

symmetry can be seen in the crystal structures. All possible C-H..π interactions are listed

in Table 1, C-H..N interactions are listed in Table 2, and also crystallographic data for the

triazines 1-3 are listed in Table 3.

Table 1. Geometrical parameters for C-H..π interactions found in the structures of 1-3.

H..Cg (Ao) C..Cg (Ao) C-H..Cg (o)

1 2.979 3.670 129.20

2.855 3.509 125.57

2.906 3.680 138.36

2.768 3.717 170.63

2.722 3.614 153.05

2 2.675 3.381 131.50

2.979 3.715 135.24

2.866 3.784 156.17

3 2.899 3.452 118.31

2.647 3.482 146.82

2.650 3.52 147.89

31

Table 2. Geometrical parameters for C-H...N hydrogen bonds in the structures of 1-3.

H..N (Ao) C..N (Ao) C-H..N (o)

1 2.68 3.35 127

2 2.94 3.66 133

2.96 3.69 134

2.40 3.34 170

2.66 3.52 150

3 2.87 3.63 137

2.88 3.69 143

2.49 3.40 160

2.72 3.61 157

Table 3. Crystallographic Data for Triazines 1-3.

1 2 3

Emp. Formula C45H42N6 C45H42N6 C45H36N6

Formula Wt. 666.85 666.85 624.77

Crystal System Monoclinic Monoclinic Monoclinic

Space Group p21/c p21/c p21/c

a (Å) 14.2520(18) 12.7264(3) 12.3563(8)

b (Å) 20.377(3) 25.8845(7) 24.1723(13)

c (Å) 13.7982(18) 11.3953(3) 11.5861(7)

α (deg) 90 90 90

β (deg) 113.493(2) 103.402(2) 102.021(4)

γ (deg) 90 90 90

Z 4 4 4

V (Å3) 3674.5(9) 3651.58(17) 3384.7(4)

Dcalc (Mg/m3) 1.2054(3) 1.2130(1) 1.2261(1)

32

1. 2,4,6-(m,m’-ditolylamino)-1,3,5-triazine (MDMETZ)

This molecule has the formula C45H42N6 and formula weight of 666.85. Crystal structure

belongs to the space group P21/c. We obtained the crystals from ethanol. Relevant

crystallographic parameters are listed in Table 3. As it can be seen from the picture

(Figure 23) the molecule does not retain trigonal symmetry in the crystalline form.

Here phenyl rings are neither planar nor perpendicular to the central ring. Dihedral angles

between the planes belonging to phenyl rings attached to same nitrogen atom are given in

Figure 23. Picture of MDMETZ molecule in crystal.

33

Table 4, and dihedral plane angles between the phenyl rings and central ring are given in

Table 5.

Table 4. MDMETZ dihedral angles between phenyl rings.

Cg Cg Alpha (o)

3 2 63.92

4 5 87.41

7 6 83.58

Table 5. MDMETZ dihedral angles between phenyl rings and central ring.

Cg Cg Alpha (o)

2 1 76.11

3 1 51.23

4 1 69.48

5 1 57.73

6 1 33.71

7 1 72.42

Figure 24 shows the arrangement of molecules within the crystal. To show the packing of

the crystals, pictures belonging to layers from all sides, view down [100] (Figure 25),

view down [010] (Figure 26), view down [001] (Figure 27) are shown in the following

pictures.

34

Figure 24. MDMETZ Hexagonal Structure.

35

Figure 25. MDMETZ crystal view down [100].

36


37

As shown in Figure 28, each MDMETZ molecule participates in two C-H…N contacts

and four C-H...π interactions. It should be noted that from this figure only two of the four

C-H...π can be seen . C-H..N interactions are shown in blue and C-H…π interactions are

shown in red color.


38

Below is the picture of the molecules that are connected by C-H...π bonding view down

[001] (Figure 29). Central molecule is related to the other four molecules by screw axis.

Even though it looks like they are all in the same plane, planes belonging to the central

rings of the central molecule and others are creating a 31-degree angle. In the plane of

paper, view down [100], they are all connected to one molecule above and one molecule

below by C-H..N H-bonding (can be seen from Figure 25). Also the angle between the

central molecule and the others and the zig-zag shape of the layer can be seen in same

picture.

Figure 28. MDMETZ interactions view down [100] (C-H..N:blue; C-H..π: red).

39

2. 2,4,6-(p,p’-ditolylamino)-1,3,5-triazine (PDMETZ)

PDMETZ molecule has the formula C45H42N6 and formula weight of 666.85. It also

belongs to centrosymmetric space group P21/c. Relevant crystallographic data is given in

Table 3. Crystals were obtained from DMF in the form of tiny needles. As it can be seen

from Figure 30, this molecule also does not retain the trigonal symmetry in the crystalline

form. Here again the phenyl rings are not in the same plane as the central ring. Dihedral

angles between the planes belonging to phenyl rings attached to same nitrogen atom are

given in Table 6, and dihedral angles between the phenyl rings and central ring are given

in Table 7. Ring 3 is unusually bent unlike other rings, presumably because of the

interactions it is making; C-H..N and C-H..π bondings in [001] direction.

Figure 29. MDMETZ view down [001].

40

Table 6. PDMETZ dihedral angles between phenyl rings.

Cg Cg Alpha (o)

3 2 72.03

4 5 73.17

7 6 80.26

Table 7. PDMETZ dihedral angles between phenyl rings and central ring.

Cg Cg Alpha (o)

2 1 54.48

3 1 75.83

4 1 47.17

5 1 69.20

6 1 55.44

7 1 47.70

Offset stacked layers of molecules can be seen in Figure 31. The centroid to centroid

distance of central rings between nearest molecules in adjacent layers is 6.921 Å; the

angle between the planes of these central rings is 14o indicating that the layers are nearly

flat. These nearest neighbors are connected to each other through three C-H...N bonds;

each molecule donates two bonds and accepts one along [001]. These two molecules are

translationally stacked along [001] and produce a columnar structure. Figures 32 and 33

show the packing of molecules along two other crystallographic axes. A view down 001

(Figure 34) shows the molecules along the column are in a zigzag arrangement. Figures

35 and 36 display the C-H…N and C-H…π contacts in the crystal structure.

41

12

34

5

67

Figure 30. PDMETZ molecule.

Figure 31. PDMETZ crystal view down [100].

42


43


44

Figure 34. PDMETZ view down [001].

45

Figure 35. PDMETZ C-H..N bonds view down [100].

[001]

[010]

46

Figure 36. PDMETZ all interactions view down [100] (C-H..N: blue; C-H..Cg: red).

[001]

[010]

47

3. 2,4,6-tris-(p-methyldiphenylamino)-1,3,5-triazine (PMETZ)

PMETZ molecule has the formula C42H36N6 and formula weight of 666.85. it crystallizes

in the centrosymmetric space group P21/c. The crystal is obtained from methanol in the

form of tiny needles. Relevant crystallographic data is given in Table 3. This crystal

structure is not completely solved yet. According to the data we obtained, molecule does

not carry over the trigonal symmetry to the crystal (Figure 37). Instead of altering phenyl

rings (one tolyl one benzyl), two tolyl rings are next to each other (numbered as 3 and 4

in Figure 37). The phenyl rings are not perpendicular to the central ring. Dihedral angles

between the planes belonging to phenyl rings attached to same nitrogen atom are given in

Table 8, and also dihedral plane angles between the phenyl rings and central ring are

given in Table 9.

Table 8. PMETZ dihedral angles between phenyl rings.

Cg Cg Alpha (o)

3 2 83.32

4 5 80.99

7 6 85.36

Table 9. PMETZ dihedral angles between phenyl rings and central ring.

Cg Cg Alpha (o)

2 1 41.54

3 1 64.83

4 1 63.71

5 1 60.47

6 1 60.68

7 1 67.69

48

The crystal structure of PMETZ is very similar to PDMETZ. Figures 38, 39, and 40

show the molecular packing along three crystallographic axes. The view down [001]

(Figure 40), illustrates that two molecules are on top of each other as in PDMETZ. These

molecules are making an angle of 16.84o between the planes of central rings. They have

6.064 Å of centroid to centroid distance belonging to central rings. Figure 41 illustrates

that molecules are in a zigzag arrangement in the column as seen in PDMETZ.

In Figure 38, molecules on top of each other are connected by C-H..N and C-H..π

interactions: along [001] it is accepting two C-H..N bonding; and in the reverse direction

it is donating two C-H..N and also donating one C-H..π (Figure 42). Through these

bonds, molecules are assembling a columnar structure as in PDMETZ.

49

Figure 37. PMETZ molecule.

1

2

3

4

5

6

7

50

Figure 38. PMETZ crystal view down [100].

51


52


53

Figure 41. Zig-zag shape formed by PMETZ molecules view down [001].

[100

[010

54

Figure 42. PMETZ all interactions (C-H..N: blue; C-H..Cg: red).

55

Experimental Section

1. General Procedure for the Synthesis of Substituted Diphenylamines In a pressure tube with stir bar, bromobenzene (8 mmol) and amine (4 mmol) were

dissolved in 20 ml Toluene. After the addition of KOt-Bu (8 mmol), purged with

Nitrogen and then the pressure tube was sealed and heated to 135 oC in an oil bath.

After 36 hours, the reaction mixture was allowed to cool to room temperature and

was quenched with 20 ml of water. The aqueous phase was extracted three times with

20 ml dichloromethane. The combined organic phases were dried over magnesium

sulfate, and the solvent was removed in vacuo. The resulting crude product was

purified by column chromatography.

p-methyldiphenylamine. Bromobenzene (1.2562 g, 8 mmol), aniline (0.36 ml, 4

mmol) and KOt-Bu (0.8977g, 8mmol) were reacted according to the general

procedure. After column chromatography (Hexane: Ethyl acetate= 19:1) product was

isolated as solid in 10% yield. Characterized by 1H NMR and 13C NMR.

2. General Procedure for the Synthesis of tris-(substituted diphenylamino)-

triazines Commercially available cyanuric chloride and the appropriate amines were used as

received without further purification. Cyanuric chloride (4 mmol) and appropriate

amine (12 mmol) were dissolved in 10 ml benzene and stirred for 2 hours. The

benzene was distilled as the sand bath temperature was raised to 200+ oC. Hydrogen

Chloride was smoothly evolved in this temperature range and the reaction was

complete in 1.5 hours.

56

2,4,6-(m,m’-ditolylamino)-1,3,5-triazine (MDMETZ). Cyanuric chloride (0.922 g,

5 mmol) and m,m’-ditolylamine (2.959 g, 15 mmol) were reacted according to the

general procedure. The flask containing the reactants was gradually heated to 290 oC

in a sand bath. Once the temperature is stabilized, the flask was gradually cooled

down to room temperature and the crude reaction product was extracted with boiling

ethanol leaving a residue of crude MDMETZ. The product was characterized by 1H

NMR (Figure 43.) and 13C NMR (Figure 44.) spectroscopy.

2,4,6-(p,p’-ditolylamino)-1,3,5-triazine (PDMETZ). Cyanuric chloride (0.3116 g,

1.69 mmol) and p,p’-ditolylamine (1.000 g, 5.07 mmol) were reacted according to the

general procedure. Temperature raised to 310 oC. Cooled down to room temperature

and crude reaction product was extracted with boiling ethanol leaving a residue of

crude PDMETZ. Characterized by 1H NMR (Figure 45.) and 13C NMR (Figure 46.).

2,4,6-tris-(p-methyldiphenylamino)-1,3,5-triazine (PMETZ). Cyanuric chloride

(0.168 g, 0.913 mmol) and p-methyldiphenylamine (0.500 g, 2.73mmol) were reacted

according to the general procedure. Temperature raised to 220 oC. Cooled down to

room temperature and crude reaction product was extracted with methanol.

Characterization was done by 1H NMR (Figure 47.) and 13C NMR (Figure 48.).

2,4,6-tris-(m-methyldiphenylamino)-1,3,5-triazine. Cyanuric chloride (1.844 g, 10

mmol) and 3-methyldiphenylamine (5.157 ml, 30 mmol) were dissolved in toluene

and refluxed for 2 hours. Distilled toluene and then raised the temperature to 200 oC

57

in 1.5 hours. Cooled to room temperature and the product washed with methanol.

Characterization was done by 1H NMR (Figure 49.) and 13C NMR (Figure 50).

2,4,6-tris-(p-hydroxydiphenylamino)-1,3,5-triazine. Cyanuric chloride (1.106 g, 6

mmol) and 4-hydroxydiphenylamine (3.33 g, 18 mmol) and potassium carbonate

(1.244 g, 9 mmol) were mixed in 50 ml toluene. Refluxed for 48 hours. Solid washed

with 200 ml hot water and then 50 ml toluene. Characterized by 1H NMR (Figure 51.)

and 13C NMR (Figure 52.).

2,4,6-tris-(m-methoxydiphenylamino)-1,3,5-triazine. Cyanuric chloride (1.844 g,

10 mmol) and 3-methoxydiphenylamine (5.977 g, 30 mmol) were dissolved in 50 ml

toluene. Refluxed for 2 hours under nitrogen. Toluene distilled and the temperature

raised to 220 oC over 1.5 hours. Cooled to room temperature and washed with

methanol. Characterization done by 1H NMR (Figure 53.) and 13C NMR (Figure 54.).

2,4,6-tris-(N-phenyl-1-naphthylamino)-1,3,5-triazine; 2,4,6-tris-(N-phenyl-2-

naphthylamino)-1,3,5-triazine; 2,4,6-tris-(p-nitrosodiphenylamino)-1,3,5-

triazine; 2,4,6-tris-(p-nitrodiphenylamino)-1,3,5-triazine and 2,4,6-tris-(m-

hydroxydiphenylamino)-1,3,5-triazine. The synthesis of these compounds was

attempted according to the general procedure; most reactions yielded several

byproducts; these products currently being purified. Also we tried to convert the

methyl groups of PDMETZ and MDMETZ to COOH groups by KMnO4 and organic

equivalent of KMnO4 (nBu4NMnO4); these reactions have not been successful.

58

Summary and Conclusion Here we showed the synthesis of diarylamines exhibiting different functional groups on

two phenyl rings. The successful attempt was in the case of phenyl-p-tolylamine, but we

believe that different diarylamines can be synthesized by this procedure without any need

of complex reaction conditions. We synthesized 2,4,6-arylamino-1,3,5-triazines both for

the purpose of as a new family, and as intermediates for further synthesis of targeted

triazines. We showed the successful coupling of diarylamines with cyanuric chloride to

obtain the targeted molecules of 2,4,6-diarylamino-1,3,5-triazines. We successfully

obtained the crystals of the products 2,4,6-(m,m’-ditolylamino)-1,3,5-triazine, 2,4,6-(p,p’-

ditolylamino)-1,3,5-triazine and 2,4,6-(phenyl-p-tolylamino)-1,3,5-triazine. By successful

retrosynthetic analysis we arrived at the targeted triazines, and showed that triazines

synthesized may be accepted as molecular analogs of ideal Piedfort units formed by

cofacial dimers of 2,4,6-arylamino-1,3,5-triazine molecules as formed in the previous

case of 2,4,6-triaryloxy-1,3,5-triazines. All the crystals obtained exhibit methyl

substituents, so far they belong to centrosymmetric space group P21/c. Though none of

the molecules retain trigonal symmetry in the crystal structures, pseudo-trigonal assembly

of molecules is identified in some cases. The assembly of molecules within the crystals

results in columnar structures formed by C-H..N and C-H..π interactions. We believe that

some other functional groups other than methyl group may give us targeted two-

dimensional noncentrosymmetric networks.

59

Figure 43. Spectrum 1. M

DM

ETZ 1H

60

Figure 44. Spectrum 2. M

DM

ETZ 13C

61

Figure 45. Spectrum 3. PD

METZ 1H

62

Figure 46. Spectrum 4. PD

METZ 13C

63

Figure 47. Spectrum 5. PM

ETZ 1H

64

Figure 48. Spectrum 6. PM

ETZ 13C

65

Figure 49. Spectrum7. M

METZ 1H

66


METZ 13C

67

Figure 51. Spectrum9. PO

HTZ 1H

68

Figure 52. Spectrum10. PO

HTZ 13C

69


MO

TZ 1H

70


MO

TZ 13C

71

REFERENCES (1) Davydov, B. L.; Derkacheva, L. D.; Dunina, V. V.; Zhabotinskii, M. E.; Zolin, V.

K.; Kereneva, L. G.; Samokhina, M.A. Connection betweencharge transfer

and laser second harmonic generation, JEPT Lett., 12, 16, 1970.

(2) Rentzepis, P. M.; Pao, Y. H. Appl. Phys. Lett,. 5, 156, 1964.

(3) Heilmer, G.H.; Ockman, N.; Braunstein, R.; Karmer, D. A. Appl. Phys. Lett,. 5,

229, 1964.

(4) Chemla, D. S.; Zyss, J. Nonlinear Optical Properties of Organic Molecules and

Crystals, Academic Press, New York, 1987.

(5) Prasad, P. N.; Williams, D. J. Introduction to Nonlinear Optical Effects in

Molecules and Polymers, John Wiley & Sons, New York, 1991.

(6) Marder, S. R.; Sohn, J. E.; Stucky, G. D. Materials for Nonlinear Optics,

American Chemical Society, Washington DC, 1991.

(7) Zyss, J. Molecular Nonlinear Optics: Materials, Physics and Devices, Academic

Press, Boston, 1993.

(8) Kanis, D. R.; Ratner, M. A.; Marks, T. J. Chem. Rev., 94, 195, 1994.

(9) Bredas, J. L.; Adant, C.; Tackx, P.; Persoons, A.; Pierce, B. M. Chem. Rev., 94,

243, 1994.

(10) Don, S. X.; Josse, D.; Zyss, J. Opt. Soc. Am. B, 10, 1708, 1993.

(11) Kodja, S.; Josse, D.; Samuel, I. D. W.; Zyss, J. Appl. Phys. Lett., 67, 3841, 1995.

(12) Franken, P. A.; Hill, A. E.; Peters, C. W.; Weinreich, W. Phys. Rev. Lett., 7, 118,

1961.

72

(13) Maiman, T. H.; Stimulated Optical Radiation in Ruby, Nature, 187, 493, 1960.

(14) Reintjes, J. F. Nonlinear Optical Parametric Processes in Liquids and Gases,

Academic Press, New York, 1984.

(15) Hanna, D. C.; Yuratich, M. A.; Cotter, D. Nonlinear Optics of Free Atoms and

Molecules, Springer-Verlag, Berlin, 1979.

(16) Zernike, F.; Midwinter, J. E. Applied Nonlinear Optics, John Wiley & Sons, New

York, 1973.

(17) Byer, R. L. Nonlinear Optical Phenomena and Materials, Annu. Rev. Mater. Sci.,

4, 147, 1974.

(18) Quder, J. L.; Hierle, R. J. Appl. Phys, 48, 2699, 1977.

(19) Zyss, J.; Chemla, D. S.; Nicoud, J. F. J. Chem. Phys., 74, 4800, 1981.

(20) Ledoux, I.; Zyss, J.; Siegel, J.; Brienne, J. S.; Lehn, J. M. Chem. Phys. Lett., 172,

440, 1990.

(21) Bredas, J. L.; Meyers, F.; Pierce, B.; Zyss, J. J. Am. Chem. Soc., 114, 4928, 1992.

(22) Joffre, M.; Yaron, D.; Silbey, R.; Zyss, J. J. Chem. Phys., 97, 5607, 1992.

(23) Zyss, J. Nonlinear Optics, 1. 3., 1991.

(24) Zyss, J.; Ledoux, I. Chem. Rev., 94, 77, 1994.

(25) Zyss, J. J. Chem. Phys., 98(9), 1993.

(26) Lee, Y. K.; Jean, S. J.; Cho, M. J. Am. Chem. Soc., 120, 10921, 1998.

(27) Lee, H.; An, S. Y.; Cho, M. J. Phys. Chem. B, 103, 4992, 1999.

(28) Cho, B. R.; Park, S. B.; Lee, S. J.; Son, K. H.; Lee, S. H.; Lee, M. J.; Yoo, J.; Lee,

Y. K.; Lee, G. J.; Kang, T. I.; Cho, M.; Jeon, S. J. J. Am. Chem. Soc., 123, 6421,

2001.

73

(29) Nalwa, H. S.; Miyata, S. Nonlinear Optics of Organic Molecules and Polymers,

Crc Press, 1997.

(30) Thalladi, V. R.; Brasselet, S.; Weiss, H.; Blaser, D.; Katz, A. K.; Carrell, H. L.;

Boese, R.; Zyss, J.; Nangia, A.; Desiraju, G. R. J. Am. Chem. Soc., 120, 2563,

1998.

(31) Li, Y. G.; Zheng, G.; Noonan, F. A. J. Org. Chem., 66, 8677, 2001.

(32) Hartwig, J. F.; Kawatsura, M.; Hauck, S. I.; Shaughnessy , K. H.; Alcazar-

Roman, L. M. J. Org. Chem., 64, 5575, 1999.

(33) Grasa, G. A.; Viciu, M. S.; Huang, J.; Nolan, S. P. J. Org. Chem., 66, 7729, 2001.

(34) Wolfe, J. P.; Tomori, H.; Sadighi, J. P.; Yin, J.; Buchwald, S. L. J. Org. Chem.,

65, 1158, 2000.

(35) Prashad, M.; Hu, B.; Lu, Y.; Draper, R.; Har, D.; Repic, O.; Blacklock, T. J. J.

Org. Chem., 65, 2612, 2000.

(36) Desmarets, C.; Schneider, R.; Fort, Y. J.Org. Chem., 67, 3029, 2002.

(37) Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc., 119, 6054, 1997.

(38) Desmarets, C.; Schneider, R.; Fort, Y.; Walcarius, A. J. Chem. Soc., Perkin

Trans. 2, 1844, 2002.

(39) Brener, E.; Schneider, R.; Fort, Y. Tetrahedron, 55, 12829, 1999.

MOLECULAR ENGINEERING OF TRIGONAL OCTUPOLAR … · 1 MOLECULAR ENGINEERING OF TRIGONAL OCTUPOLAR...

Documents

Transcript of MOLECULAR ENGINEERING OF TRIGONAL OCTUPOLAR … · 1 MOLECULAR ENGINEERING OF TRIGONAL OCTUPOLAR...